Integrated circuit (IC) chips provide for electrical connections to/from their circuitry via specialized structures known as “bond pads” that reside on the IC. These bond pads typically have sufficient areas (e.g., dimensions typically greater than 50 micrometer by 50 micrometers, relatively large areas compared to other features on the chip) of exposed metal that facilitate conductive physical attachment of either conductive metal wires or conductive metal trace features which electrically connect the chip to its package and off-chip circuitry (including the external electric power the chip needs to operate).
FIG. 1 depicts a prior art bond pad structure suitable for the attachment of small wire to bond pad via physical “wire bonding” that is known in the art. The electrical signal flows through the wire, through the physically bonded joint with the bond pad, and then through the bond pad thickness to thin film patterned metal interconnect into the rest of the integrated circuit. Typically, the bond pad metal film is thicker than the thickness of other metal films in the IC to protect the underlying dielectric from damage incurred during the probe-testing and wire bonding process.
The prior art bond pad 120 resides on top of an insulating dielectric layer 140 as shown in FIGS. 1A and 1B that serves to electrically isolate the physical bond pad from the semiconductor chip 150 except through electrical connection to the metal layer 110 to elsewhere on the chip than the lateral bond pad region. As is known in the art, often the first semiconductor devices in the electrical signal path between the bond pad and the rest of the chip circuitry is a device structure that provides protection of the IC from electrostatic discharge (ESD) that can often occur as electronics are further handled and assembled into larger systems. In some prior art cases, the bond pad may be part of the ESD protection device. While there is abundant prior art that describes thin-film IC bond pads suitable for operation of conventional ICs designed to function over normal electronics temperature ranges (i.e., about −55° C. to about 125° C.), prior art bond pads fail to meet the highly challenging demands imposed by greatly expanding the peak operational temperature to 500° C. and beyond. In particular, the materials and structures employed in conventional IC bond pads cannot durably withstand extreme IC temperature ranges (−55° C. to 500° C.) without severe physical damage and degradation that impede desired electrical functionality (conductivity) of the bond pad structure. For example, the greatly increased temperature range imposes larger physical stresses on metal and insulator thin-film stack/structure used to form prior-art bond pad structures (such as FIGS. 1A and 1B) because the metal thin film(s) and dielectric thin film(s) have differing thermal expansion properties (i.e., different coefficients of thermal expansion (CTE)). These thermally-sensitive stress forces build across the relatively large-area interface between the wire bonding metal and insulator until one of the films suffers irreversible physical damage in the form of cracks, buckling, or de-lamination that degrades the bond pad electrical functionality. In silicon, creep of the semiconductor itself under stress and temperature can also occur leading to bond pad degradation and failure. Another failure mechanism that becomes more active at higher temperatures is oxidation of the metal and sensitive metal-to-metal or metal-to-semiconductor interfaces, which typically turns desirably conductive IC bond pad into undesirably non-conductive metal oxide. When oxygen reaches stressed interfaces of dissimilar materials through a crack in the protective dielectric, lateral enhancement/acceleration of oxidation along the interface and resulting degradation of electrical conduction properties can occur leading to accelerated device failure. While there are many different variants of conventional bond pads in the prior art, they are all susceptible to similar damage mechanisms as IC operational temperature ranges are expanded to reach towards 500° C. and beyond operating temperatures.